1. Field of the Invention
The invention relates to a control system that is applied to an engine that is provided with a plurality of injection valves capable of supplying fuel into the same cylinder.
2. Description of Related Art
In Japanese Patent Application Publication No. 2006-214415 (JP 2006-214415 A), there is described an exemplary engine that is provided, for each cylinder, with a first injection valve that injects fuel into an intake passage and a second injection valve that directly injects fuel into a combustion chamber. A fuel supply system of this engine is equipped with a common path that is connected to a fuel tank, a first supply path that is connected to a downstream end of the common path, and a second supply path that is connected to the downstream end of the common path. Fuel is supplied to the first injection valve through the first supply path, and fuel is supplied to the second injection valve through the second supply path. Moreover, in the case where an injection sharing ratio is a value obtained by dividing an amount of fuel injection from the first injection valve by a sum of the amount of fuel injection from the first injection valve and an amount of fuel injection from the second injection valve, a control device for the engine controls the respective injection valves by setting the injection sharing ratio to a value corresponding to an operating state of the engine.
Incidentally, the engine described in Japanese Patent Application Publication No. 2006-214415 (JP 2006-214415 A) is an engine that can be operated through the use of alcohol-containing fuel. The injection sharing ratio is changed in accordance with the concentration of alcohol in fuel.
By the way, even when the interior of the fuel tank is refueled with new fuel as fresh fuel, old fuel, that is, the fuel used prior to refueling remains in both the first supply path and the second supply path. Therefore, for a while even after refueling, even when either the first injection valve or the second injection valve is driven, old fuel is injected from the injection valve. When old fuel is thus injected from the injection valve, the amount of old fuel remaining in the supply path gradually decreases, and the interior of the supply path is soon filled with new fuel. When the interior of the supply path is thus filled with new fuel, new fuel is injected from the injection valve.
It should be noted herein that the volume of the first supply path and the volume of the second supply path are generally different from each other. Therefore, the timing when the interior of the first supply path is filled with new fuel and the timing when the interior of the second supply path is filled with new fuel are unlikely to coincide with each other. That is, although old fuel still remains in one of the first supply path and the second supply path, the interior of the other supply path is likely to be filled with new fuel. Then, for example, under the situation where old fuel still remains in the second supply path even when the interior of the first supply path is filled with new fuel, new fuel is injected from the first injection valve, whereas old fuel is injected from the second injection valve. On the contrary, under the situation where old fuel still remains in the first supply path even when the interior of the second supply path is filled with new fuel, new fuel is injected from the second injection valve, whereas old fuel is injected from the first injection valve.